In an air brake for a vehicle, particularly a truck or a semi trailer, the expansion of an air chamber by actuation of a brake pedal causes a shaft positioned on two bushing assemblies located adjacent to the wheel axle to rotate. The rotation of the shaft rotates an S-cam located at the outboard end of the shaft. Brake shoes which are held in contact with the S-cam are urged outwardly by the rotation of the S-cam and its shape. The outward motion of the brake shoes places brake liners mounted on the brake shoes into frictional engagement with a brake drum of the wheel hub, resulting in braking of the wheel mounted on the hub.
The shaft is an area of concern in maintaining the air brakes. It is important to be able to remove the shaft for maintenance, particularly without removing the wheel hub. It is also important to be able to remove and maintain the bushings which permit the rotation of the shaft while holding it in fixed position relative to the axle. The first of the bushings is located near the inboard end of the shaft near the brake actuator, and it is generally referred to in this invention as the "inboard bushing". The second of the bushings is located at the brake spider, where the shaft typically passes through a boss in the spider. Since this second bushing is located towards the outboard end of the shaft, we refer to it in this application as the "outboard bushing" or as the "spider bushing". While some of the problems with the bushings are shared by both bushings, there are other problems which are unique to each of the bushings. One problem in the art is wear surface contamination in the bushing, particularly the bushing nearer the brake spider. The present invention is focused on the outboard or spider bushing.